This post, like many of my others on the topic ramble a bit. You have been warned :P
Any regular readers I might have will know how much I like Pimsleur products for learning experience. I believe the basic idea can be greatly enhanced with computers. I did in fact try a short time ago but suffered from a lack of voice talent which is where speech synthesis could be useful.
Synthesised voices can be imported into the current system (which at the moment I wouldn’t be able to demonstrate since the voices need to be licensed if they are to be distributed) just by recording them to audio. This solution would allow maximum support since any browser with audio capabilities could use the system.
There is an advantage to using the IE plugin though (or any other system supporting SALT) - speech recognition. It should be entirely possible to actually have a browser based system that checks your pronunciation which would instantly make it better than any system out there.
Quite why none of the companies that create these synthetic voices have tried to develop a system like this I don’t know…